In the uplink of Long Term Evolution (LTE) as a next generation mobile communication standard, just one codeword is transmitted through an antenna. The physical uplink shared channel (PUSCH) is used for the uplink data transmission in such a system, and the Uplink Control Information (UCI) including channel quality indicator (CQI), rank indicator (RI), and hybrid automatic repeat request—acknowledgement (HARQ-ACK) is carried in the same PUSCH transmitted for the uplink data.
FIG. 1 is a diagram illustrating a procedure for processing data and UCI in the uplink of a legacy LTE system on the transport channel and physical channel levels. In FIG. 1, reference numbers 101 to 110 denote the steps of processing on the transport channel, and reference numbers 111 to 115 denote the steps of processing on the physical channel.
In the uplink of the legacy LTE system, a User Equipment (UE) uses a single codeword and a single antenna such that, when the PUSCH and UCI are transmitted together, the UCI is mapped to a single codeword and then transmitted on a single layer.
Referring to FIG. 1, the UE determines a number of coded symbols for the transmission of ACK or RI, i.e., the number of symbols for RI (channel coding RI) at step 107 and the number of symbols for ACK (channel coding ACK/NACK) at step 108. The UE also determines the number of coded symbols for transmitting CQI in the PUSCH, i.e., the number of symbols for CQI (channel coding CQI) at step 106.
The UE attaches a Cyclic Redundancy Check (CRC) to the Transport Block (TB) at step 101 and segments the TB into code blocks and attaches the CRC to each code block again at step 102. Next, the UE performs channel coding at step 103, rate matching at step 104, and then concatenates the code blocks (channel block concatenation) at step 105. Next, the UE multiplexes data (UL-SCH data) and CQI information (data and control multiplexing) at step 109.
Next, the UE performs interleaving (channel interleaving) on the data uplink shared channel (UL-SCH) data, CQI, RI, and ACK/NACK information (that are processed at steps 109, 107, and 108) at step 110.
FIG. 2 is a diagram illustrating uplink (UL) channel interleaver-layer mapping relationship in the legacy LTE system. In FIG. 2, reference number 201 denotes an exemplary symbol configuration of the UL channel interleaver, and reference number 202 denotes an exemplary symbol configuration of layer#1. Referring to FIG. 2, the output bit sequence of the channel interleaver as denoted by reference number 201 is mapped one by one onto the layer#1 as denoted by reference number 202.
The channel interleaved information is scrambled at step 111, modulated (modulation mapper) at step 112, transformed by discrete Fourier transform (DFT) (transform precoder, DFT) at step 113, mapped to resource (resource element mapper) at step 114, and then transformed by inverse fast Fourier transform (IFFF) for transmission at step 115.
In the LTE system, the UE uses a single codeword and a single antenna for uplink transmission as described above such that, when the data and UCI are transmitted together in the PUSCH, the UCI is transmitted on the signal layer as mapped to the single codeword.
Unlike the legacy LTE system, the UE can use two codewords and up to four transmit antennas in LTE-Advanced (LTE-A) system. Accordingly, when the data and UCI are transmitted together through UL-SCH, the UCI can be mapped to one or two codewords. This means that the UE can transmit the UCI on multiple layers in the uplink of the LTE-A system.
However, in the case in which the transmitted UCI is unequally distributed on the two layers, if the channel status is good for one layer but bad for the other, the UCI reception performance is likely degraded especially when such control information is concentrated onto the layer having bad channel status.